The typo3/html-sanitizer package is an HTML sanitizer, written in PHP, aiming to provide XSS-safe markup based on explicitly allowed tags, attributes and values. Due to a parsing issue in the upstream package masterminds/html5, malicious markup used in a sequence with special HTML comments cannot be filtered and sanitized. This allows for a bypass of the cross-site scripting mechanism of typo3/html-sanitizer. This issue has been addressed in versions 1.0.7 and 2.0.16 of the typo3/html-sanitizer package. Users are advised to upgrade. There are no known workarounds for this issue.